Polyoxymethylene resin composition

ABSTRACT

A polyoxymethylene resin composition comprising: 
     (A) 50 to 99 parts by weight of a polyoxymethylene resin; 
     (B) 1 to 50 parts by weight of a wollastonite having a volume-average particle diameter of 0.5 to 40 μm; 
     (C) 0.1 to 10 parts by weight of at least one member selected from the group consisting of an ester of an alcohol and a fatty acid, an ester of an alcohol and a dicarboxylic acid, and a compound of a polyoxyalkylene glycol based on 100 parts by weight of the total amount of Component (A) and Component (B); and 
     (D) 0.1 to 10 parts by weight of a polyolefin resin based on 100 parts by weight of the total amount of Component (A) and Component (B). 
     The composition of the present invention provides a molded product which is excellent in resistance to friction and wearing, has high stiffness, repeated impact strength, and small molding strain, and is excellent in gear precision as compared with conventional compositions. Therefore, the polyoxymethylene resin composition of the present invention can be provided as a new material for the electrical and electronic parts, down-sizing of which has been progressing.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP99/00757 which has an Internationalfiling date of Feb. 22, 1999, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to a polyoxymethylene resin compositionand the molded product thereof, which exhibits excellent resistance tofriction and wearing, high stiffness, high repeated impact strength, andsmall molding strain, and is excellent in gear precision.

BACKGROUND ART

A polyoxymethylene resin has been widely used as an engineering resinhaving well-balanced mechanical properties and excellent moldability infields such as automobile parts, electrical and electronic products,etc. In the field of electrical and electronic products, downsizing andlightening of products have been recently proceeding. As a result, thepolyoxymethylene resin is required, not only for further improvement instiffness and resistance to friction and wearing, but also forimprovement in impact strength, molding strain and gear precision.

For the purpose of improving stiffness and resistance to friction andwearing, techniques of incorporating an inorganic filler, a lubricantand the like with a polyoxymethylene resin have been proposed. JapanesePatent Publication Unexamined No. 1-263145 (corresponding to U.S. Pat.No. 5,106,896) discloses a technique of adding inorganic powder having amean particle diameter of 100 μm or less and an ester of mono- orpoly-valent alcohol and fatty acid to a polyacetal resin. JapanesePatent Publication Unexamined No. 3-111446 (corresponding to U.S. Pat.No. 5,173,532) discloses a resin composition obtainable by incorporatingwith a polyacetal resin a graft copolymer wherein an olefin polymer anda vinyl or ether polymer are chemically bonded in a branch orcross-linking structure, a lubricant, and inorganic powder having a meanparticle diameter of 100 μm or less. These prior art documents do notexemplify, as the inorganic filler, wollastonite which is one of thecomponents of the present invention; therefore, they are totallyinsufficient in improvement of stiffness and resistance to friction andwearing. Japanese Patent Publication Unexamined No. 5-51514 discloses atechnique of adding spindle-shaped calcium carbonate and an ester ofmono- or poly-valent alcohol and fatty acid to a polyacetal resin, butthis is also insufficient in improving stiffness and resistance tofriction and wearing. Japanese Patent Publication Unexamined No.7-157630 discloses a composition comprising a graft or block copolymerobtained from olefin polymers and at least one of vinyl polymers, fattyester, inorganic powder having a mean particle diameter of 30 μm or lessand potassium titanate whisker, and a polyacetal resin. The compositiondisclosed therein is sufficient in improving stiffness, but is stillinsufficient in improving resistance to friction and wearing. Further,it has a drawback that molding strain (warpage of a molded product) islarge.

On the other hand, techniques using wollastonite for a polyoxymethyleneresin are described in Japanese Patent Publication Unexamined No.49-21451 (corresponding to U.S. Pat. No. 3,775,363) which discloses anintimate mixture comprising 98 to 25 parts by weight of apolyoxymethylene resin and 2 to 75 parts by weight of needle-likecalcium metasilicate without using a coupling agent. This composition isimproved in processability, thermal stability and dimensional accuracycompared with the case using a glass fiber. Japanese Patent PublicationUnexamined No. 61-120848 (corresponding to U.S. Pat. No. 4,645,785)discloses a composition having high resistance to wearing comprising 40to 94.7 parts by weight of a polyoxymethylene, 5 to 50 parts by weightof wollastonite, 0.2 to 5 parts by weight of N-hydroxymethylmelamine,0.1 to 5 parts by weight of silicone oil having a polymerization degreeof 10 to 5,000, 0.1 to 10 parts by weight of polyethylene or a copolymerof ethylene and α-olefin having a molecular weight of 100,000 to1,000,000. It is observed that this composition is improved inresistance to friction and wearing with metals, but the resistance tofriction and wearing with a polyoxymethylene resin or the samecomposition, which is to be necessary for practical use, is considerablyinsufficient. Japanese Patent Publication Unexamined No. 64-43555(corresponding to U.S. Pat. No. 4,987,176) discloses a compositioncontaining polyoxymethylene polymers, wollastonite having a meanthickness of 5 μm or less and a mean length/thickness ratio of 5 ormore, and if necessary additives, and a production method thereof.Further, this prior art specifically discloses, as additives, melaminessuch as N-hydroxymethylmelamine, silicone oil having a polymerizationdegree n of 10 to 5,000 and a polyethylene and/or a copolymer ofethylene and α-olefin having a molecular weight of 100,000 to 1,000,000,and this prior art further discloses as more preferable additives,stabilizers, nucleating agents, antistatic agents, light stabilizers,flame-retardants, lubricants, plasticizers, pigments, dyes, thermalstabilizers, and mold release agents. However, this prior art does notteach specific examples of lubricants. The composition disclosed in thisprior art purposes improving mechanical strength.

DESCRIPTION OF THE INVENTION

The present inventors have made studies about adding various inorganicfillers, lubricants and other resin components to a polyoxymethyleneresin. As a result, they accomplished the present invention by finding acomposition which comprises (A) a polyoxymethylene resin, (B)wollastonite, (C) at least one member selected from the group consistingof an ester of (i) an alcohol and a fatty acid, (ii) an ester of analcohol and a dicarboxylic acid, and (iii) a compound of apolyoxyalkylene glycol, and (D) a polyolefin resin, whereby saidcomposition exhibits excellent resistance to friction and wearing, highstiffness, high repeated impact strength, and small molding strain, andis excellent in gear precision.

Accordingly, the present invention relates to a polyoxymethylene resincomposition comprising:

(A) 50 to 99 parts by weight of a polyoxymethylene resin;

(B) 1 to 50 parts by weight of a wollastonite having a volume-averageparticle diameter of 0.5 to 40 μm;

(C) 0.1 to 10 parts by weight of at least one member selected from thegroup consisting of (i) an ester of an alcohol and a fatty acid, (ii) anester of an alcohol and a dicarboxylic acid, and (iii) a compound of apolyoxyalkylene glycol based on 100 parts by weight of the total amountof Component (A) and Component (B); and

(D) 0.1 to 10 parts by weight of a polyolefin resin based on 100 partsby weight of the total amount of Component (A) and Component (B).

Further, the present invention relates to a molded product prepared bymolding the above composition, particularly working parts such as agear, a cam, a slider, a lever, an arm, a clutch, a joint, an axis, abearing, a key-stem and a key-top, outsert resinous parts for a chassis,a chassis, a tray and a side plate, which are used for office automationapparatuses represented by a printer and a copying machine; for videoapparatuses represented by a video tape recorder (VTR) and a video movie(a video camera); for apparatuses for music, image, or informationrepresented by a cassette player, a laser disc (LD), a mini disc (MD), acompact disc (CD) [including CD-ROM (read only memory), CD-R(recordable) and CD-RW (rewritable)], a digital video disc (DVD)[including DVD-ROM, DVD-R, DVD-RAM (random access memory) andDVD-Audio], a navigation system and a mobile personal computer; fortelecommunication apparatuses represented by a cellular phone and afacsimile machine; for an interior or exterior working part for anautomobile; and for industrial miscellaneous goods represented by adisposable camera, a toy, a fastener, a conveyor, a buckle, and anapparatus for house-building.

BEST MODE FOR CARRYING OUT THE INVENTION

The polyoxymethylene resins used for Component (A) of the presentinvention are homopolymers prepared by polymerizing formaldehyde or acyclic oligomer thereof such as trioxane, a trimer of formaldehyde, andtetraoxane, a tetramer of formaldehyde, and by blocking terminals of thepolymer with an ether group or an ester group; copolymers prepared bycopolymerizing formaldehyde, its trimer of trioxane or its tetramer oftetraoxane with comonomers such as ethylene oxide, propylene oxide,1,3-dioxolan and 1,4-butanediol formal; copolymers thereof which furtherhave branched molecular chains; polyoxymethylene block copolymers, ofwhich one terminal is blocked with different type of components such aspolyethylene glycol; and the like.

The polyoxymethylene resins used in the present invention has a meltindex (MI) (measured under the conditions prescribed by ASTM-D 1238-57T)of 0.1 g/10 min to 150 g/10 min, preferably 1 g/10 min to 100 g/10 min.The copolymer type polyoxymethylene contains the comonomers in an amountof 0.1 to 20 mol, preferably 0.3 to 10 mol, based on 100 mol ofoxymethylene.

The polyoxymethylene resin of the present invention can contain a heatstabilizer, a weathering (light) stabilizer or a combination of thesestabilizers for use. Of course, the polyoxymethylene resin can bepreliminarily stabilized with these stabilizers.

As the heat stabilizer, an antioxidant and a catching agent offormaldehyde or formic acid are preferable. A combination of these heatstabilizers is also effective. As the antioxidants, a hindered phenoltype antioxidant is preferable. For example, the hindered phenol typeantioxidant includesn-octadecyl-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)-propionate,n-octadecyl-3-(3′-methyl-5′-t-butyl-4′-hydroxyphenyl)-propionate,n-tetradecyl-3-(3′,5′-di-t-butyl-4′-hydroxyphdnyl)-propionate,1,6-hexanediol-bis-(3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate),1,4-butanediol-bis-(3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate),triethyleneglycol-bis-(3-(3-t-butyl-S-methyl-4-hydroxyphenyl)-propionate),tetrakis-(methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionatemethane,3,9-bis(2-(3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy)-1,1-dimethylethyl)2,4,8,10-tetraoxaspiro(5,5)undecane,N,N′-bis-3-(3′,5′-di-t-butyl-4-hydroxyphenol)propionylhexamethylenediamine,N,N′-tetramethylenebis-3-(3′-methyl-5′-t-butyl-4-hydroxyphenol)propionyldiamine,N,N′-bis-(3-(3,5-di-t-butyl-4-hydroxyphenol)propionyl)hydrazine,N-salicyloyl-N′-salicylidene hydrazine,3-(N-salicyloyl)amino-1,2,4-triazol,N,N′-bis(2-(3-(3,5-di-butyl-4-hydroxyphenyl)propionyloxy)ethyl)oxyamido,and the like. Of these hindered phenol type antioxidants, triethyleneglycol-bis-(3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate),tetrakis-(methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionatemethaneare preferable.

As the catching agents of formaldehyde and formic acid, there can beexemplified (a) compounds and polymers containing formaldehyde-reactivenitrogen, (b) a hydroxide, an inorganic acid salt, a carboxylic acidsalt or an alkoxide, and the like of an alkali metal or an alkali earthmetal.

As (a) the compounds containing formaldehyde-reactive nitrogen, therecan be exemplified (1) dicyan diamide, (2) an amino-substitutedtriazine, (3) a co-condensation product of an amino-substituted triazineand formaldehyde, and the like. (2) an amino-substituted triazineincludes, for instance, guanamine(2,4-diamino-sym-triazine),melamine(2,4,6-triamino-sym-triazine), N-butylmelamine,N-phenylmelamine, N,N-diphenylmelamine, N,N-diallylmelamine,N,N′,N″-triphenylmelamine, N-methylolmelamine, N,N′-dimethylolmelamine,N,N′,N″-trimethylolmelamine,benzoguanamine(2,4-diamino-6-phenyl-sym-triazine),2,4-diamino-6-methyl-sym-triazine, 2,4-diamino-6-butyl-sym-triazine,2,4-diamino-6-benzyloxy-sym-triazine, 2,4-diamino-6-butoxy-sym-triazine,2,4-diamino-6-cyclohexyl-sym-triazine,2,4-diamino-6-chloro-sym-triazine, 2,4-diamino-6-mercapto-sym-triazine,2,4-dioxy-6-amino-sym-triazine, 2-oxy-4,6-diamino-sym-triazine,N,N′,N′-tetracyanoethylbenzoguanamine, and the like. (3) aco-condensation product of an amino-substituted triazine andformaldehyde includes, for instance, a melamine-formaldehydepolycondensation product, and the like. Of these, dicyan diamide,melamine and a melamine-formaldehyde polycondensation product arepreferable.

Further, as (a) the polymer containing a formaldehyde-reactive nitrogengroup, there can be exemplified (1) a polyamide resin, (2) a polymerobtained by polymerizing acrylamide and/or a derivative thereof, oracrylamide and/or a derivative thereof and other vinyl monomers in thepresence of metal alcolate, (3) a polymer obtained by polymerizingacrylamide and/or a derivative thereof, or acrylamide and/or aderivative thereof and other vinyl monomers in the presence of a radicalpolymerization initiator, and (4) a polymer containingnitrogen-containing groups such as an amine, an amide, urea andurethane. As (1) a polyamide resin, there can be exemplified nylon 4-6,nylon 6, nylon 6-6, nylon 6-10, nylon 6-12, nylon 12 and copolymersthereof such as nylon 6/6-6, nylon 6/6-6/6-10 and nylon 6/6-12. As (2) apolymer obtained by polymerizing acrylamide and/or a derivative thereof,or acrylamide and/or a derivative thereof and other vinyl monomers inthe presence of metal alcolate, a poly-β-alanine copolymer can beexemplified. These polymers can be prepared according to the methodsdisclosed in Japanese Patent Publication Examined No. 6-10259(corresponding to U.S. Pat. No. 5,015,707), Japanese Patent PublicationExamined No. 5-87096, Japanese Patent Publication Examined No. 5-47568and Japanese Patent Publication Unexamined No. 3-234729. (3) a polymerobtained by polymerizing acrylamide and/or a derivative thereof, oracrylamide and/or a derivative thereof and other vinyl monomers in thepresence of a radical polymerization initiator can be prepared accordingto the method disclosed in Japanese Patent Publication Unexamined No.3-28260 (corresponding to U.S. Pat. No. 5,011,890).

(b) The hydroxide, the inorganic acid salt, the carboxylic acid salt orthe alkoxide of an alkali metal or an alkali earth metal includes, forinstance, hydroxide of such as sodium, potassium, magnesium, calcium andbarium, and carbonate, phosphate, silicate, borate and carboxylate ofthe above metals. The carboxylic acid of the carboxylate is saturated orunsaturated aliphatic carboxylic acids having 10 to 36 carbon atoms, andthe like. And, these carboxylic acids may be substituted with hydroxylgroups. As the saturated aliphatic carboxylic acids, a capric acid, alauric acid, a myristic acid, a palmitic acid, a stearic acid, anarachic acid, a behenic acid, a lignoceric acid, a cerotic acid, amontanoic acid, a melissic acid and a lacceric acid can be exemplified.As the unsaturated aliphatic carboxylic acids, an undecylenic acid, anoleic acid, an elaidic acid, cetoleic acid, an erucic, acid, a brassidicacid, a sorbic acid, a linoleic acid, a linolenic acid, an arachidonicacid, a propiolic acid, a stearolic acid and the like can beexemplified. Further, as an alkoxide, a methoxide, an ethoxide and thelike of the above-exemplified metals can be illustrated as examples.

As the weathering (light) stabilizers, (a) benzotriazole typesubstances, (b) anilide oxalate type substances and (c) hindered aminetype substances are preferable. As (a) the benzotriazole typesubstances, there can be exemplified, for instance,2-(2′-hydroxy-5′-methyl-phenyl)benzotriazole,2-(2′-hydroxy-3,5-di-t-butyl-phenyl)benzotriazole,2-(2′-hydroxy-3,5-di-t-amyl-phenyl)benzotriazole,2-[2′-hydroxy-3,5-bis-(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole,2-(2′-hydroxy-5′-octylphenyl)benzotriazole, and the like. Of these,2-[2′-hydroxy-3,5-bis-(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole and2-(2′-hydroxy-3,5-di-t-butyl-phenyl)benzotriazole are preferable.

As (b) the anilide oxalate type substances, there can be exemplified,for instance, 2-ethoxy-2′-ethyloxalic acid bisanilide,2-ethoxy-5-t-butyl-2′-ethyloxalic acid bisanilide,2-ethoxy-3′-dodecyloxalic acid bisanilide, and the like. Thesesubstances may be used alone or in combination.

As (c) the hindered amine type substances, there can be exemplified4-acetoxy-2,2,6,6-tetramethylpiperidine,4-stearoyloxy-2,2,6,6-tetramethylpiperidine,4-acryloyloxy-2,2,6,6-tetramethylpiperidine,4-(phenylacetoxy)-2,2,6,6-tetramethylpiperidine,4-benzoyloxy-2,2,6,6-tetramethylpiperidine,4-methoxy-2,2,6,6-tetramethylpiperidine,4-stearyloxy-2,2,6,6-tetramethylpiperidine,4-cyclohexyloxy-2,2,6,6-tetramethylpiperidine,4-benzyloxy-2,2,6,6-tetramethylpiperidine,4-phenoxy-2,2,6,6-tetramethylpiperidine,4-(ethylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine,4-(cyclohexylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine,4-(phenylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine,bis(2,2,6,6-teteramethyl-4-piperidine)-carbonate,bis(2,2,6,6-tetramethyl-4-piperidyl)-oxalate,bis(2,2,6,6-tetramethyl-4-piperidyl)-malonate,bis(2,2,6,6-teteramethyl-4-piperidyl)-sebacate,bis(2,2,6,6-teteramethyl-4-piperidyl)-adipate,bis(2,2,6,6-teteramethyl-4-piperidyl)-terephthalate,1,2-bis(2,2,6,6-teteramethyl-4-piperidyloxy)-ethane,α-α′-bis(2,2,6,6-teteramethyl-4-piperidyloxy)-p-xylene,bis(2,2,6,6-teteramethyl-4-piperidyl)tolylene-2,4-dicarbamate,bis(2,2,6,6-teteramethyl-4-piperidyl)-hexamethylene-1,6-dicarbamate,tris(2,2,6,6-tetramethyl-4-piperidyl)-benzene-1,3,5-tricarboxylate,tris(2,2,6,6-tetramethyl-4-piperidyl)-benzene-1,3,4-tricarboxylate andthe like, preferably bis(2,2,6,6-tetramethyl-4-piperidyl)-sebacate.These hindered amine type substances may be used individually or incombination. Further, the combination of at least one of thebenzotriazole type substances and the anilide oxalate type substanceswith the hindered amine type substances is most preferable.

The wollastonite used for Component (B) of the present invention isprepared by generally pulverizing wollastonite existing in the nature orsynthetic wollastonite. In this pulverizing process, wollastonite in theshape of a long thin needle and a particle (including a short stick anda granule) is obtained. These wollastonites may be in the shape of aneedle or a particle, or in combination of these shapes. The particlediameter is in the range of 0.5 to 40 μm, preferably 1 to 30 μm, in avolume-average particle diameter. The particle diameter of over 40 μmunfavorably causes deterioration of surface appearance and slidingproperty of the resin. The particle diameter of less than 0.5 μmunfavorably causes deterioration of processability since the improvementeffect of stiffness is reduced and the viscosity at melting isincreased.

The granular wollastonite has an aspect ratio of preferably 2 to 7, morepreferably 3 to 5. When the aspect ratio is lower than 2, the stiffnessis not improved effectively. When it is higher than 7, the warpage isapt to become large. The needle-like wollastonite has an aspect ratio ofpreferably 10 to 30, more preferably 10 to 25. When an aspect ratio islower than 10, the stiffness is not improved effectively. When it ishigher than 30, the warpage is apt to become large.

Either wollastonite with a treated surface or with an untreated surfacemay be used. As the surface treatment agents, conventionally known onescan be used; for instance, various types of coupling agents such assilane type, titanate type, aluminum type and zirconium type can beused. Specifically, the useful coupling agents includeN-(2-aminoethyl)-3-aminopropyl triethoxysilane, 3-glycidoxypropyltrimethoxysilane, isopropyl trisstealoyl titanate, diisopropoxy ammoniumethylacetate, n-butylzirconate, and the like.

The wollastonite is added in an amount of 1 to 50 parts by weight,preferably 2 to 40 parts by weight, more preferably 5 to 30 parts byweight, based on 100 parts by weight of the resin comprising thepolyoxymethylene type resin and the wollastonite. When it is less than 1part by weight, the reinforcing effect of the filler is not exhibitedsufficiently. When it is more than 50 parts by weight, not only thedeterioration in the surface appearance but also reduction in moldingprocessability and impact strength are unfavorably caused.

The ester of an alcohol and a fatty acid, the ester of an alcohol and adicarboxylic acid and the polyoxyalkylene glycol compound used asComponent (C) of the present invention are as follows.

The ester of an alcohol and a fatty acid includes esters of an alcoholand a fatty acid listed below.

The alcohol includes a monovalent alcohol and a polyvalent alcohol. Themonovalent alcohol includes, for instance, saturated or unsaturatedalcohol such as methyl alcohol, ethyl alcohol, propyl alcohol, butylalcohol, amyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol,nonyl alcohol, decyl alcohol, undecyl alcohol, lauryl alcohol, tridecylalcohol, myristyl alcohol, pentadecyl alcohol, cetyl alcohol, heptadecylalcohol, stearyl alcohol, oleyl alcohol, nonadecyl alcohol, eicosylalcohol, ceryl alcohol, behenyl alcohol, melissyl alcohol, hexyldecylalcohol, octyldodecyl alcohol, decylmyristyl alcohol, and decylstearylalcohol.

The polyvalent alcohol includes, for instance, ethylene glycol,diethylene glycol, triethylene glycol, propylene glycol, dipropyleneglycol, butane diol, pentane diol, hexane diol, glycerin, diglycerin,triglycerin, pentaerythritol, arabitol, ribitol, xylitol, sorbite,sorbitan, sorbitol, mannitol, and the like.

The fatty acid includes caproic acid, enanthic acid, caprylic acid,pelargonic acid, capric acid, undecyl acid, lauric acid, tridecyl acid,myristic acid, pentadecyl acid, palmitic acid, pentadecyl acid, stearicacid, nanodecanoic acid, arachic acid, behenic acid, lignoceric acid,cerotic acid, heptacosanoic acid, montanoic acid, melissic acid,lacceric acid, undecylenic acid, oleic acid, elaidic acid, cetoleicacid, erucic acid, brassidic acid, sorbic acid, linoleic acid, linolenicacid, arachidonic acid, propiolic acid, stearolic acid, and the like.Further, the fatty acid includes natural fatty acids containing theabove-listed components or a mixture thereof. These fatty acids may besubstituted with a hydroxy group. Among the above-listed esters of analcohol and a fatty acid, an ester of an alcohol and a fatty acidindependently having a carbon number of 10 or more is preferable fromthe viewpoint of improvement in resistance to friction and wearing; anester of a fatty acid having a carbon number of 12 or more and analcohol having a carbon number of 10 or more is more preferable; and anester of a fatty acid having a carbon number of 12 to 30 and an alcoholhaving a carbon number of 10 to 20 is more preferable.

The ester of an alcohol and a dicarboxylic acid includes the monoesterand diester of a saturated or unsaturated primary alcohol such as octylalcohol, nonyl alcohol, decyl alcohol, undecyl alcohol, lauryl alcohol,tridecyl alcohol, myristyl alcohol, pentadecyl alcohol, cetyl alcohol,heptadecyl alcohol, stearyl alcohol, oleyl alcohol, nonadecyl alcohol,eicosyl alcohol, ceryl alcohol, behenyl alcohol, melissyl alcohol,hexyldecyl alcohol, octyldodecyl alcohol, decylmyristyl alcohol anddecylstearyl alcohol and a dicarboxylic acid such as oxalic acid,malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, maleic acid and fumaric acid,and a mixture thereof.

Of these esters of an alcohol and a dicarboxylic acid, an acid of analcohol and a dicarboxylic acid having independently a carbon number of10 or more is preferable.

As the polyoxymethylene glycol compound, three types of the compound areexemplified. A first group of the compound includes a polycondensationproduct containing an alkylene glycol as a monomer, for example, apolyethylene glycol, a polypropylene glycol and a block polymer ofethylene glycol and propylene glycol. The polymerization degree of thesecompounds is preferably 5 to 1,000, more preferably 10 to 500. A secondgroup is an etherified compound of the first group of compounds and analiphatic alcohol, for example, polyethylene glycol oleyl ether(ethyleneoxide polymerization degree: 5 to 50), polyethylene glycolcetyl ether (ethyleneoxide polymerization degree: 5 to 50), polyethyleneglycol stearyl ether (ethyleneoxide polymerization degree: 5 to 30),polyethylene glycol lauryl ether (ethyleneoxide polymerization degree: 5to 30), polyethylene glycol tridecyl ether (ethyleneoxide polymerizationdegree: 5 to 30), polyethylene glycol nonylphenyl ether (ethyleneoxidepolymerization degree: 2 to 100), polyethylene glycol octylphenyl ether(ethyleneoxide polymerization degree: 4 to 50), and the like. A thirdgroup of compounds is an etherified compound of the first group ofcompounds and a higher fatty acid, for example, polyethylene glycolmonolaurate (ethyleneoxide polymerization degree: 2 to 30), polyethyleneglycol monostearate (ethyleneoxide polymerization degree: 2 to 50),polyethylene glycol monooleate (ethyleneoxide polymerization degree: 2to 50), and the like.

Among the above-listed Component (C), an ester of an alcohol and a fattyacid and an ester of an alcohol and a dicarboxylic acid are preferablyused in view of resistance to friction and wearing.

These esters of lubricants are contained in an amount of 0.1 to 10 partsby weight, preferably 0.2 to 5 parts by weight, based on the totalamount of 100 parts by weight of (A) the polyoxymethylene resin and (B)the wollastonite. If the addition amount of the lubricants is less than0.1 part by weight, the improvement in the sliding propertiesunfavorably becomes insufficient. If it is more than 10 parts by weight,the reduction of mechanical properties becomes unfavorably remarkable.

The polyolefin resin used for Component (D) of the present invention isa homopolymer, a copolymer of an unsaturated olefinic compoundrepresented by the general formula (1) or a modified product thereof:

wherein R₁ represents a hydrogen atom or a methyl group; and R₂represents a hydrogen atom, an alkyl group or a carboxyl group, having acarbon number of 1 to 10, an alkylated carboxyl group having a carbonnumber of 2 to 5, an acyloxyl group having a carbon number of 2 to 5, ora vinyl group.

Specifically, a polyethylene (a high-density polyethylene, amedium-density polyethylene, a high-pressure low-density polyethylene, alinear low-density polyethylene and an ultra-low-density polyethylene),a polypropylene, an ethylene-propylene copolymer, an ethylene-butenecopolymer, a polypropylene-butene copolymer, a polybutene, ahydrogenated product of a polybutadiene, an ethylene-acrylic estercopolymer, an ethylene-methacrylic ester copolymer, an ethylene-acrylicacid copolymer, an ethylene-vinyl acetate copolymer, and the like areexemplified. As modified products thereof, graft copolymers prepared bygrafting one or more other vinyl compounds can be exemplified.

Of these, a polyethylene (a high-pressure low-density polyethylene, alinear low-density polyethylene and an ultra-low-density polyethylene),an ethylene-propylene copolymer, and an ethylene-butene copolymer arepreferable. A weight-average molecular weight of these polyolefin typeresins is not particularly restricted, but preferably 10,000 to 300,000,more preferably 10,000 to 100,000, further more preferably 15,000 to80,000. When the weight-average molecular weight is lower than 10,000,the resistance to friction and wearing with the same material as of thepresent invention are caused to be unfavorably deteriorated. When it ishigher than 300,000, the resistance to friction and wearing with thepolyoxymethylene resin are caused to be unfavorably deteriorated.

The polyolefin polymer is added in an amount of 0.1 to 10 parts byweight, preferably 0.2 to 5 parts by weight, based on 100 parts byweight of a resin comprising (A) the polyoxymethylene resin and (B) thewollastonite. When the addition amount of the polyolefin polymer is 0.1or less, the improvement of the sliding properties unfavorably becomesinsufficient. When it is more than 10 parts by weight, the moldedproduct is unfavorably peeled off.

For the polyoxymethylene resin composition of the present invention,there can be employed crystalline nucleating agents, antistatic agents,mold release agents, inorganic fillers other than wollastonite andpigments, which are not described in the present specification but havebeen conventionally and widely used for the polyoxymethylene resins.

The pigments include inorganic and organic ones. The inorganic pigmentsmean those commonly used for coloring resins, for example, they includezinc sulfide, zinc oxide, titanium oxide, barium sulfate, titan yellow,iron oxide, ultramarine, cobalt blue, a carbonate, a phosphate, anacetate, carbon black, acetylene black, lamp black, and the like. Theorganic pigments include pigments in the types of, for example, azo,isoindolin, disazo, monoazo, anthraquinone, heterocyclic, perinone,quinacridone, thioindigo, perylene, dioxazine, phthalocyanine, and thelike.

Melt kneading methods of the polyoxymethylene resin composition of thepresent invention are not particularly limited. Generally, the resincomposition is melt kneaded with a monoaxial extruder or a biaxialextruder. At this time, a processing temperature is preferably 180 to240° C. Further, the ways of feeding each component upon the extrusionare not particularly limited. For instance, the components may be fedaccording to the methods: (1) mixing the polyoxymethylene resin, awollastonite, a lubricant and a polyolefin resin all at once and feedingthe mixture from the main feeder of an extruder to melt knead; (2)feeding the polyoxymethylene resin and an additive from the main feederof an extruder and then feeding a wollastonite to a molten resin from aside feeder provided at the middle of the extruder to melt knead; (3)feeding and kneading an additive agent after the polyoxymethylene resinand wollastonite are melt kneaded; or the like.

EXAMPLES

Hereinafter, the present invention is illustrated in detail referring toExamples. First of all, components and evaluation methods employed inExamples and Comparative Examples are described below.

Description of Component Used

A. Polyoxymethylene Resin

A-1: Polyoxymethylene copolymer containing 4 mol % of ethylene oxide asa comonomer and having a melt index of 30 g/10 min (ASTM D-1238-57T)[further containing 0.4% by weight of triethyleneglycol-bis-(3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate), 0.1% byweight of melamine and 0.05% by weight of nylon 6,6 as a stabilizer].

A-2: Polyoxymethylene homopolymer having a melt index of 30 g/10 min(ASTM D-1238-57T) [further containing 0.4% by weight of triethyleneglycol-bis-(3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate) and 0.5%by weight of poly-β-alanine having a volume-average particle diameter of2.5 μm as a stabilizer].

A-3: Block copolymer of polyoxymethylene homopolymer and polyethyleneglycol having a melt index of 30 g/10 min (ASTM D-1238-57T) [furthercontaining 0.4% by weight of triethyleneglycol-bis-(3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate) and 0.5%by weight of poly-β-alanine having a volume-average particle diameter of2.5 μm as a stabilizer].

A-4: Polyoxymethylene copolymer containing 2 mol % of 1,3-dioxolan as acomonomer and having a melt index of 30 g/10 min (ASTM D-1238-57T)[further containing 0.4% by weight of triethyleneglycol-bis-(3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate), 0.4% byweight of melamine and 0.05 % by weight of nylon 6,6 as a stabilizer].

B. Wollastonite and Others

B-1: Needle-like wollastonite having a volume-average particle diameterof 6 μm measured with a laser particle diameter measuring device, and ashorter diameter of 2 μm and a longer diameter of 40 μm measured with ascanning electron microscope.

B-2: Needle-like wollastonite having a volume-average particle diameterof 15 μm measured with a laser particle diameter measuring device, and ashorter diameter of 4.5 μm and a longer diameter of 50 μm measured witha scanning electron microscope.

B-3: Granular wollastonite having a volume-average particle diameter of3 μm measured with a laser particle diameter measuring device and havingan aspect ratio of 3.

B-4: Granular wollastonite having a volume-average particle diameter of10 μm measured with a laser particle diameter measuring device andhaving an aspect ratio of 5.

B-5: Granular wollastonite having a volume-average particle diameter of20 μm measured with a laser particle diameter measuring device andhaving an aspect ratio of 5.

B-6: Granular wollastonite having a volume-average particle diameter of50 μm measured with a laser particle diameter measuring device andhaving an aspect ratio of 5.

B-7: Granular talc having a volume-average particle diameter of 6 μmmeasured with a laser particle diameter measuring device and having anaspect ratio of 5.

B-8: Granular calcium carbonate having a volume-average particlediameter of 3 μm measured with a laser particle diameter measuringdevice and having an aspect ratio of 3.

B-9: Potassium titanate whisker having a shorter diameter of 0.15 μm anda longer diameter of 20 μm measured with a scanning electron microscope.

C. Lubricant (Ester of Alcohol and Fatty Acid, etc.)

C-1: Cetyl myristate

C-2: Stearyl stearate

C-3: Adipic acid dilaurate

C-4: Ethylene glycol distearate

C-5: Polyethylene glycol (polymerization degree=30)

C-6: Liquid ethylene-propylene copolymer (molar ratio ofethylene/propylene =50/50; polymerization degree n=55)

D. Polyolefin Resin

D-1: Ethylene-butene copolymer (MI=70 g/10 min; Mw=50,000)

D-2: Ethylene-butene copolymer (MI=18 g/10 min; Mw=70,000)

D-3: Ethylene-butene copolymer (MI=3.6 g/10 min; Mw=100,000)

D-4: Ethylene-butene copolymer (MI=0.3 g/10 min; Mw=190,000)

D-5: High-pressure low-density polyethylene (MI=45 g/10 min; Mw 49,000)

D-6: High-pressure low-density polyethylene (MI=0.4 g/10 min;Mw=280,000)

D-7: Ethylene-butene copolymer (MI=150 g/10 min; Mw=20,000)

D-8: High-pressure low-density polyethylene (MI=90 g/10 min; Mw=24,000)

D-9: High density polyethylene (MI=0.3 g/10 min; Mw=190,000)

Evaluation Method

(1) Evaluation of Physical Properties

i) Melt Flow Rate (MI): Measured according to ASTM D-1238-57T

ii) Tensile Strength (TS) and Tensile Elongation (TE): Measuredaccording to ASTM D638

iii) Flexural Strength (FS) and Flexural Modulus (FM): Measuredaccording to ASTM D790

iv) Izod Impact Strength (Izod): Measured according to ASTM D256

(2) Repeated Impact Strength

In order to measure Izod impact strength, a specimen was preparedaccording to ASTM D256 and subjected to a repeated impact test under theconditions of a load of 160 g, a drop height of 20 mm and a drop rate of35 drops/min to count a number until the specimen was broken using arepeated impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd.

(3) Molding Strain

Pellets obtained in Examples and Comparative Examples were dried at 80°C. for three hours, and then molded into a plate having a size of 150mm×150 mm and a thickness of 3 mm (wherein a 1 mm pin gate existed ateach side of the plate, the position of which was on the center line ofthe plate and 20 mm away from the edge) under the conditions of a moldtemperature of 70° C. and a cooling period of 30 seconds using a 5-ouncemolding machine (IS-100E manufactured by Toshiba Machine Co., Ltd.)whose cylinder temperature was set at 200° C. The resultant plate wasleft for 2 days after molding, and then was placed on a flat desk. Aweight was put on an edge without the pin gate of the plate so as forthe other edge to rise from the surface of the desk. The height the edgerose was measured using a micrometer. The measured height was defined asfollows:

⊚: 1 mm or less

∘: more than 1 mm, and 2 mm or less

Δ: more than 2 mm, and 5 mm or less

X: more than 5 mm, and 10 mm or less

XX: more than 10 mm

(4) Sliding Properties

Pellets obtained in Examples and Comparative Examples were dried at 80°C. for three hours, and then molded into a plate having a thickness of 3mm under the conditions of a mold temperature of 70° C. and a coolingperiod of 20 seconds using a 1-ounce molding machine (TI-30Gmanufactured by Toyo Machinery and Metal Co., Ltd.) whose cylindertemperature was set at 200° C. to prepare a specimen. Using areciprocating friction and wearing tester (AFT-15MS type manufactured byTosoku Seimitsu Co., Ltd.), the friction coefficient and abrasion wear(maximum depth of wear) of the plate specimen were measured byreciprocating an SUS304 material (a ball with a 5 mm diameter) andpolyacetal resin materials (cylinders with a 5 mm diameter and a tipR=2.5 mm which were molded respectively using Tenac® 4520 and thepolyacetal resin composition of the present invention) 5,000 times onthe surface of the plate specimen under the conditions of a load of 2kg, a linear speed of 30 mm/sec, a reciprocating distance of 20 mm andan environmental temperature of 23° C.

(5) Intermeshing Test

A gear having a module of 1.0 mm, a tooth number of 30, a pressure angleof 20 degrees and a thickness of 5 mm was molded using a 1-ounceinjection. molding machine, of which the cylinder temperature was set at200° C., at a mold temperature of 80° C. Then, 1 pitch meshing error ofboth tooth flanks was measured according to Japan Gear MachineryAssociation Standard, JGMA 116-02.

Example 1

80 parts by weight of (A-1) polyoxymethylene copolymer, 20 parts byweight of (B-1) wollastonite, 2 parts by weight of (C-1) ester ofalcohol and fatty acid and 2 parts by weight of (D-1) polyolefin resinwere uniformly mixed using a Henschel mixer. The resultant mixture wasfed to a 30 mm biaxial extruder having L/D=30 through a main feedingport, and kneaded at a screw rotation number of 100 rpm with anextrusion amount of 10 kg/hr. The extruded resin was cut into pelletsusing a strand cutter, and the resultant pellets were subjected tovarious evaluations. The results thereof are shown in Table 1.

Examples 2 to 5

The same procedure as in Example 1 was carried out except that (B1)employed in Example 1 was changed to (B-2) to (B-5) as shown in Table 1.The results thereof are shown in Table 1.

Comparative Examples 1 to 3

The same procedure as in Example 1 was carried out except that (B-1)employed in Example 1 was changed to (B-6) to (B-8) as shown in Table 1.The results thereof are shown in Table 1.

As is apparent from the comparison between Examples 3 to 5 andComparative Example 1, the repeated impact strength and resistance tofriction and wearing were deteriorated when the particle diameter of awollastonite exceeded the range claimed in the present invention.

As is apparent from the comparison between Examples 3 to 5 andComparative Example 2, the resin containing talc was inferior to thosecontaining a granular wollastonite in molding strain, pitch meshingerror of both tooth flanks, repeated impact strength and resistance tofriction and wearing, though the stiffness was almost the same.

Further, as is apparent from the comparison between Examples 3 to 5 andComparative Example 3, the resin containing calcium carbonate wasinferior to those containing a granular wollastonite in stiffness,repeated impact strength and resistance to friction and wearing, thoughmolding strain and pitch meshing error of both tooth flanks were almostsame.

Comparative Examples 4 and 5

The same procedure as in Example 1 was carried out except that theamount of (A-1) employed in Example 1 was changed and (B-1) was changedto (B-9), an amount of which was further changed as shown in Table 1.The results thereof are shown in Table 1.

As is apparent from the comparison between Examples 1 and 2 andComparative Examples 4 and 5, the resin containing potassium titanatewhisker was inferior to that containing a needle-like wollastonite inmolding strain, pitch meshing error of both tooth flanks, repeatedimpact strength and resistance to friction and wearing.

Comparative Example 6

The same procedure as in Example 1 was carried out except that (D-1)employed in Example 1 was not added. The results thereof are shown inTable 1.

As is apparent from the comparison with Example 1, when the polyolefinresin was not contained, the properties of resistance to friction andwearing with stainless steel were good, but those with apolyoxymethylene resin and with the same material as of the presentinvention were not improved.

Comparative Example 7

The same procedure as in Example 1 was carried out except that (C-1)employed in Example 1 was not added. The results thereof are shown inTable 1.

As is apparent from the comparison with Example 1, when a lubricant suchas a fatty ester was not contained, the resistance to friction andwearing were not improved.

Comparative Example 8

The same procedure as in Example 1 was carried out except that (C-1) and(D-1) employed in Example 1 were not added. The results thereof areshown in Table 1.

As apparent from the comparison with Example 1, when a lubricant such asfatty ester and a polyolefin resin were not contained, the resistance tofriction and wearing were considerably inferior.

Examples 6 to 13

The same procedure as in Example 1 was carried out except that (D-1)employed in Example 1 was changed to (D-2) to (D-9) as listed in Table2. The results thereof are shown in Table 2.

Examples 14 to 17

The same procedure as in Example 3 was carried out except that (C-1)employed in Example 3 was changed to (C-2) to (C-5) as listed in Table2. The results thereof are shown in Table 2.

Examples 18 and 19

The same procedure as in Example 1 was carried out except that (B-1)employed in Example 1 was changed to a mixture of (B-1) and (B-3) shownin Table 2. The results thereof are shown in Table 2.

Example 20

80 parts by weight of (A-2) polyoxymethylene homopolymer, 20 parts byweight of (B-1) wollastonite, 2 parts by weight of (C-1) ester ofalcohol and fatty acid, 2 parts by weight of (D-2) polyolefin resin wereuniformly mixed using a Henschel mixer. The resultant mixture was fed toa 30 mm biaxial extruder having L/D=30 and being set at 190° C. throughits main feeding port, and kneaded at a screw rotation number of 100 rpmwith an extrusion amount of 8 kg/hr. The extruded resin was cut intopellets using a strand cutter, and the resultant pellets were subjectedto various evaluation. The results thereof are shown in Table 3.

Examples 21 and 22

The same procedure as in Example 20 was carried out except that (C-1)employed in Example 20 was changed to (C-3) or (C-5) as shown in Table3. The results thereof are shown in Table 3.

Example 23

The same procedure as in Example 20 was carried out except that (B-1)employed in Example 20 was changed to (B-3) as shown in Table 3. Theresults thereof are shown in Table 3.

Example 24

The same procedure as in Example 21 was carried out except that (B-1)employed in Example 21 was changed to (B-3) as shown in Table 3. Theresults thereof are shown in Table 3.

Example 25

The same procedure as in Example 20 was carried out except that (A-2)employed in Example 20 was changed to (A-3). The results thereof areshown in Table 3.

Example 26

The same procedure as in Example 23 was carried out except that (A-2)employed in Example 23 was changed to (A-3). The results thereof areshown in Table 3.

Example 27

The same procedure as in Example 20 was carried out except that (A-2)employed in Example 20 was changed to a mixture of (A-2) and (A-3) andfurther Component (C-6) was added in an amount of 3 parts by weight. Theresults thereof are shown in Table 3.

Example 28

The same procedure as in Example 27 was carried out except that (B-1)employed in Example 27 was changed to (B-3). The results thereof areshown in Table 3.

Example 29

The same procedure as in Example 27 was carried out except that (B-1)employed in Example 27 was changed to a mixture of (B-1) and (B-3). Theresults thereof are shown in Table 3.

Example 30

80 parts by weight of (A-1) polyoxymethylene copolymer, 2 parts byweight of (C-1) and 2 parts by weight of (D-2) were uniformly mixedusing a Henschel mixer. The resultant mixture was fed to a 30 mm biaxialextruder having L/D=30 and being set at 200° C. through its main feedingport, and 20 parts by weight of (B-1) wollastonite was fed from a sidefeeding port provided downstream of the main feeding port. Then,kneading was carried out at a screw rotation number of 100 rpm. Theamount ratio of main feeding to side feeding was controlled according toeach weight ratio and the final amount of extrudate was adjusted so asto be 8 kg/hr. The extruded resin was cut into pellets using a strandcutter. Using the resultant pellets, evaluation was carried out. Theresults thereof are shown in Table 3.

Example 31

The same procedure as in Example 30 was carried out except that (B-1)employed in Example 30 was changed to (B-3). The results thereof areshown in Table 3.

Example 32

80 parts by weight of (A-4) polyoxymethylene copolymer was fed from themain feeding port of a 60 mm biaxual extruder having L/D=40 and beingset at 200° C. 10 parts by weight of (B-1) wollastonite was fed from aside feeding port-1 provided downstream of the main feeding port.Further, a mixture prepared by uniformly kneading 10 parts by weight of(A-4) polyoxymethylene copolymer, 2 parts by weight of (C-1) ester ofalcohol and fatty acid and 2 parts by weight of (D-1) polyolefin using aHenschel mixer was fed from a side feeding port-2 provided downstream ofthe side feeding port-1. Then, kneading was carried out at a screwrotation number of 150 rpm. The amount ratio of main feeding to sidefeeding was controlled according to each weight ratio and the finalamount of extrudate was adjusted so as to be 150 kg/hr. The screw wasdesigned so as to arrange that the components added at the previous stepwere in a completely melted and uniformly mixed state at each of theside feeding ports. The extruded resin was cut thereafter into pelletswith a strand cutter. Using the resultant pellets, evaluation wascarried out. The results thereof are shown in Table 4.

Example 33

The same procedure as in Example 32 was carried out except. that theamount of (A-4) fed from the main feeding port was changed to 70 partsby weight and that of (B-1) fed from the side feeding port-1 was changedto 20 parts by weight. The results thereof are shown in Table 4.

Example 34

The same procedure as in Example 32 was carried out except that theamount of (A-4) fed from the main feeding port was changed to 60 partsby weight, that of (B-1) fed from the side feeding port-1 was changed to30 parts by weight and that of (D-2) fed from the side feeding port-2was changed to 3 parts by weight. The results thereof are shown in Table4.

Example 35

The same procedure as in Example 33 was carried out except that (B-1)was changed to (B-3) and (C-1) was changed to (C-3). The results thereofare shown in Table 4.

Example 36

The same procedure as in Example 34 was carried out except that (B-1)was changed to (B-3) and (C-1) was changed to (C-3). The results thereofare shown in Table 4.

TABLE 1 Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex.3 Ex. 4 Ex. 5 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8Composition Polyoxymethylene resin 80 80 80 80 80 80 80 80 95 90 80 8080 (A-1) Wollastonite, etc. (B-1) 20 20 20 20 (B-2) 20 (B-3) 20 (B-4) 20(B-5) 20 (B-6) 20 (B-7) 20 (B-8) 20 (B-9) 5 10 Aliphatic ester, etc.(C-1) 2 2 2 2 2 2 2 2 2 2 2 0 0 Polyoefin resin (D-1) 2 2 2 2 2 2 2 2 22 0 2 0 Result Physical Property MI (g/10 min) 25 25 24 25 27 29 28 2422 22 25 23 20 TS (kg/cm²) 540 540 510 520 520 520 520 480 520 590 530640 690 TE (%) 6 7 7 6 6 6 6 7 6 5 7 5 5 FS (kg/cm²) 950 960 900 920 910920 910 860 880 990 970  1100  1200 FM (kg/cm²) 44100 45100 34000 3500036000 38000 36000 32000 34000 49000 45000 45000 46000 Izod (kg · cm/cm)3.5 3.5 3.6 3.5 3.5 3.5 3.4 3.7 3.4 3.3 3.6 3.5 3.7 Repeated impactstrength  1200  1100  2000  1900  1700  1200 900 500 900 500  1000  1200   1100 (number) Molding strain ◯ ◯ ⊚ ⊚ ⊚ ⊚ ◯ ⊚ X XX ◯ ◯ ◯ Meshingerror of 0.025 0.029 0.015 0.018 0.023 0.040 0.030 0.015 0.055 0.085 — —— both tooth flanks (mm) Resistance to Friction & Weaving Stainlesssteel Friction coefficient (μ) 0.11 0.15 0.15 0.16 0.18 0.28 0.48 0.480.14 0.18 0.10 0.70 0.71 Abrasion wear (μm) 5 5 5 6 8 30 120 150 18 28 4290 340 Polyoxymethylene resin Friction coefficient (μ) 0.12 0.12 0.210.21 0.22 0.35 0.47 0.58 0.20 0.20 0.51 0.45 0.68 Abrasion wear (μm) 1918 35 36 40 78 140 190 73 40 130 110 230 Own material Frictioncoefficient (μ) 0.16 0.15 0.16 0.17 0.19 0.32 0.30 0.35 0.16 0.16 0.740.58 0.75 Abrasion wear (μm) 23 21 32 40 41 74 98 130 74 33 230 190 280

TABLE 2 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex.15 Ex. 16 Ex. 17 Ex. 18 Ex. 19 Composition Polyoxy- 80 80 80 80 80 80 8080 80 80 80 80 80 80 methylene resin (A-1) Wollastonite, etc. (B-1) 2020 20 20 20 20 20 20 10 15 (B-3) 20 20 20 20 10 5 Aliphatic ester, etc.(C-1) 2 2 2 2 2 2 2 2 2 2 (C-2) 2 (C-3) 2 (C-4) 2 (C-5) 2 Polyolefinresin (D-1) 2 2 2 2 2 2 (D-2) 2 (D-3) 2 (D-4) 2 (D-5) 2 (D-6) 2 (D-7) 2(D-8) 2 (D-9) 2 Result Pysical Property MI (g/10 min) 24 25 24 24 25 2626 24 24 25 28 28 25 25 TS (kg/cm²) 540 530 540 540 550 540 540 540 520520 500 500 530 540 TE (%) 7 6 6 6 6 7 6 6 7 7 8 8 7 6 FS (kg/cm²) 950960 970 970 960 960 970 960 900 900 880 890 940 950 FM (kg/cm²) 4400044000 44000 45000 45000 44000 45000 44000 34000 34000 33000 33000 4000043000 Izod 3.5 3.4 3.5 3.4 3.6 3.5 3.5 3.2 3.5 3.5 3.3 3.4 3.5 3.5 (kg ·cm/cm) Repeated im-  1200  1100 900  1200 800  1100  1100 800  2000 2000  2000  2000  1600  1300 pact strength (number) Molding strain ◯ ◯◯ ◯ ◯ ◯ ◯ ◯ ⊚ ⊚ ⊚ ⊚ ⊚ ◯ Meshing error 0.025 0.025 0.027 0.025 0.0270.023 0.023 0.025 0.015 0.015 0.016 0.014 0.017 0.020 of both toothflanks (mm) Resistance to Friction & Wearing Stainless steel Friction0.11 0.12 0.14 0.12 0.14 0.12 0.12 0.20 0.16 0.15 0.19 0.18 0.15 0.13coefficient (μ) Abrasion wear 6 6 12 6 14 6 8 26 8 7 13 15 5 5 (μm)Polyoxy- methylene resin Friction 0.12 0.12 0.26 0.12 0.28 0.14 0.140.33 0.20 0.18 0.19 0.25 0.16 0.14 coefficient (μ) Abrasion wear 20 2642 22 50 26 25 67 30 28 33 44 25 20 (μm) Own material Friction 0.16 0.160.20 0.15 0.19 0.20 0.18 0.30 0.17 0.19 0.22 0.20 0.16 0.16 coefficient(μ) Abrasion wear 25 25 42 25 51 27 30 70 32 35 45 45 27 21 (μm)

TABLE 3 Ex. 20 Ex. 21 Ex. 22 Ex. 23 Ex. 24 Ex. 25 Ex. 26 Ex. 27 Ex. 28Ex. 29 Ex. 30 Ex. 31 Composition Polyoxymethylene resin (A-1) 80 80(A-2) 80 80 80 80 80 40 40 40 (A-3) 80 80 40 40 40 Wollastonite, etc.(B-1) 20 20 20 20 20 15 20 (B-3) 20 20 20 20 5 20 Aliphatic ester, etc.(C-1) 2 2 2 2 2 2 2 2 2 (C-3) 2 2 (C-5) 2 (C-6) 3 3 3 Polyolefin resin(D-2) 2 2 2 2 2 2 2 2 2 2 2 2 Result Physical Property MI (g/10 min) 2425 25 25 25 27 27 28 29 28 26 27 TS (kg/cm²) 600 610 590 570 560 510 510560 530 550 610 540 TE (%) 6 6 6 6 6 6 7 6 6 6 5 6 FS (kg/cm²)  1040 960 1030 980 990 920 910 970 940 950  1050 890 FM (kg/cm²) 50000 5000049000 38000 38000 44000 45000 46000 37000 43000 51000 40000 Izod (kg ·cm/cm) 3.6 3.5 3.4 3.6 3.5 3.5 3.5 3.5 3.6 3.5 3.5 3.4 Repeated impactstrength (number)  1100  1100  1100  2100  2000  1100  1100  1100  2000 1300  1200  2100 Molding strain ◯ ◯ ◯ ⊚ ⊚ ◯ ⊚ ◯ ⊚ ⊚ ◯ ⊚ Meshing errorof both tooth flanks 0.026 0.027 0.027 0.016 0.017 0.026 0.016 0.0220.014 0.018 0.025 0.014 (mm) Resistance to Friction & Wearing Stainlesssteel Friction coefficient (μ) 0.09 0.10 0.18 0.16 0.16 0.13 0.19 0.090.15 0.10 0.10 0.15 Abrasion wear (μm) 5 6 10 8 10 8 13 5 6 5 4 5Polyoxymethylene resin Friction coefficient (μ) 0.14 0.15 0.19 0.20 0.210.11 0.18 0.11 0.15 0.13 0.11 0.20 Abrasion wear (μm) 25 26 25 33 38 1728 18 20 16 15 30 Own material Friction coefficient (μ) 0.16 0.18 0.190.18 0.19 0.15 0.16 0.13 0.15 0.14 0.15 0.16 Abrasion wear (μm) 20 24 3030 35 24 28 15 20 15 18 25

TABLE 4 Ex. 32 Ex. 33 Ex. 34 Ex. 35 Ex. 36 Composition Polyoxymethyleneresin 90 80 70 80 70 (A-4) Wollastonite, etc. (B-1) 10 20 30 (B-3) 20 30Aliphatic ester, etc. (C-1) 2 2 2 (C-3) 2 2 Polyolefin resin (D-1) 2 2 32 2 Result Physical Property MI (g/10 min) 24 20 15 25 17 TS (kg/cm²)590 680 780 530 590 TE (%) 6 5 4 6 5 FS (kg/cm²)  1040  1200  1400 940 1010 FM (kg/cm²) 44000 63000 82000 38500 45000 Izod (kg · cm/cm) 3.63.5 3.4 3.5 3.2 Repeated impact strength  1400  1200  1000  2100  1500(number) Molding strain ◯ ◯ ◯ ⊚ ⊚ Meshing error of both 0.018 0.0260.029 0.015 0.017 tooth flanks (mm) Resistance to Friction & WearingStainless steel Friction coefficient (μ) 0.09 0.09 0.05 0.13 0.10Abrasion wear (μm) 5 3 2 6 5 Polyoxymethylene resin Friction coefficient(μ) 0.14 0.11 0.10 0.19 0.15 Abrasion wear (μm) 25 12 10 25 20 Ownmaterial Friction coefficient (μ) 0.16 0.15 0.12 0.17 0.16 Abrasion wear(μm) 20 15 10 18 20

INDUSTRIAL APPLICABILITY

The polyoxymethylene resin composition of the present invention providesa molded product which is excellent in resistance to friction andwearing, has high stiffness, repeated impact strength, and small moldingstrain, and is excellent in gear precision as compared with conventionalcompositions. Therefore, the polyoxymethylene resin composition of thepresent invention can be provided as a new material for electrical andelectronic parts, down-sizing of which has been progressing.

For example, the polyoxymethylene resin composition of the presentinvention can be used for parts of office automation apparatusesrepresented by a printer and a copying machine; for parts of videoapparatuses represented by a VTR and a video movie (a video camera); forparts of apparatuses for music, image, or information represented by acassette player, an LD, an MD, a CD (including CD-ROM, CD-R and CD-RW),a DVD (including DVD-ROM, DVD-R, DVD-RAM and DVD-Audio), a navigationsystem and a mobile personal computer; for parts of telecommunicationapparatuses represented by a cellular phone and a facsimile machine; foran interior or exterior working part of an automobile; and for parts ofindustrial miscellaneous goods represented by a disposable camera, atoy, a fastener, a conveyor, a buckle and an apparatus forhouse-building.

As the above-listed parts of various apparatuses, there can bespecifically exemplified working parts such as a gear, a cam, a slider,a lever, an arm, a clutch, a joint,. an axis, a bearing, a key-stem anda key-top, outsert resinous parts for a chassis, a chassis, a tray, aside plate, and the like.

What is claimed is:
 1. A polyoxymethylene resin composition comprising:(A) 50 to 99 parts by weight of a polyoxymethylene resin; (B) 1 to 50parts by weight of a wollastonite having a volume-average particlediameter of 0.5 to 40 μm; (C) 0.1 to 10 parts by weight of at least onemember selected from the group consisting of an ester of an alcohol anda fatty acid, an ester of an alcohol and a dicarboxylic acid, and acompound of a polyoxyalkylene glycol based on 100 parts by weight of thetotal amount of Component (A) and Component (B); and (D) 0.1 to 10 partsby weight of a polyolefin resin based on 100 parts by weight of thetotal amount of Component (A) and Component (B): wherein when Component(C) is an ester of alcohol and a dicarboxylic acid, the alcohol is asaturated or unsaturated primary alcohol selected from the groupconsisting of at least one of octyl alcohol, nonyl alcohol, decylalcohol, undecyl alcohol, lauryl alcohol, tridecyl alcohol, myristylalcohol, pentadecyl alcohol, cetyl alcohol, heptadecyl alcohol, stearylalcohol, oleyl alcohol, nonadecyl alcohol, eicosyl alcohol, cerylalcohol, behenyl alcohol, melissyl alcohol, hexyldecyl alcohol,octyldodecyl alcohol, decylmyristyl alcohol and decylstearyl alcohol. 2.A polyoxymethylene resin composition. according to claim 1, wherein theshape of the wollastonite of Component (B) is at least one memberselected from the group consisting of a granular shape and a needle-likeshape.
 3. A polyoxymethylene resin composition according to claim 1 or2, wherein the ester of an alcohol and a fatty acid of Component (C) isan ester of an alcohol and a fatty acid having independently a carbonnumber of not less than 10, the ester of an alcohol and a dicarboxylicacid of Component (C) is an ester of an alcohol and a dicarboxylic acid,each having independently not less than 10 carbon atoms, and thecompound of a polyoxyalkylene glycol of Component (C) is at least onemember selected from the group consisting of (1) at least one memberselected from the group consisting of a polyethylene glycol, apolypropylene and a block copolymer of a polyethylene glycol and apolypropylene glycol which independently have the polymerization degreeof 5 to 1,000, (2) an etherified compound of the compound described in(1) and an aliphatic compound, and (3) an esterified compound of thecompound described in (1) and a higher fatty acid.
 4. A polyoxymethyleneresin composition according to claim 1, wherein the polyolefin resin ofComponent (D) is at least one member selected from the group consistingof a homopolymer or a copolymer of an unsaturated olefinic compound asrepresented by the general formula (1) as described below, or a modifiedproduct thereof:

wherein R₁ represents a hydrogen atom or a methyl group; and R₂represents a hydrogen atom, an alkyl group or a carboxyl group having 1to 10 carbon atoms, an alkylated carboxyl group having 2 to 5 carbonatoms, an acyloxyl group having 2 to 5 carbon atoms, or a vinyl group.5. A polyoxymethylene resin composition according to claim 1, whereinthe polyolefin resin of Component (D) is at least one member selectedfrom the group consisting of a high-pressure low-density polyethylene, alinear low-density polyethylene, an ultra-low-density polyethylene, anethylene-propylene copolymer, and an ethylene-butene copolymer, and theweight-average molecular weight thereof is in the range of 10,000 to300,000.
 6. A polyoxymethylene resin composition according to claim 5,wherein the polyolefin resin of Component (D) has a weight-averagemolecular weight in the range of 10,000 to 100,000.
 7. A molded productobtainable by molding the polyoxymethylene resin composition accordingto claim
 1. 8. At least one part selected from the group consisting of aworking part, an outsert resinous part for a chassis, a chassis, a tray,and a side plate, which are obtained by molding, cutting, or molding andcutting the polyoxymethylene resin composition according to claim
 1. 9.A part according to claim 8, wherein the working part is at least onepart selected from the group consisting of a gear, a cam, a slider, alever, an arm, a clutch, a joint, an axis, a bearing, a key-stem, and akey-top.
 10. A part according to claim 8 or 9, which is used for officeautomation apparatuses represented by a printer, and a copying machine.11. A part according to claim 8 or 9, which is used for videoapparatuses represented by a video tape recorder, and a video movie (avideo camera).
 12. A part according to claim 8 or 9, which is used forapparatuses for music, for image, or for information represented by acassette player, a laser disc, a mini disc, a compact disc (includingCD-ROM, CD-R and CD-RW), digital video disc (including DVD-ROM, DVD-R,DVD-RAM and DVD-Audio), a navigation system, and a mobile personalcomputer.
 13. A part according to claim 8 or 9, which is used fortelecommunication apparatuses represented by a cellular phone, and afacsimile machine.
 14. A part according to claim 8 or 9, which is usedfor an interior or exterior working part for an automobile.
 15. A partaccording to claim 8 or 9, which is used for industrial miscellaneousgoods represented by a disposable camera, a toy, a fastener, a conveyor,a buckle, and an apparatus for house-building.
 16. A polyoxymethyleneresin composition according to claim 1, wherein the wollastonite ofComponent (B) has a volume-average particle diameter of 1-30 μm.
 17. Apolyoxymethylene resin composition according to claim 1, wherein thewollastonite of Component (B) is added in an amount of 2 to 40 parts byweight based upon 100 parts by weight of Component (A) and Component(B).
 18. A polyoxymethylene resin composition according to claim 1,wherein the wollastonite of Component (B) has a volume-average particlediameter of 1-30 μm, and is added in an amount of 2 to 40 parts byweight based upon 100 parts by weight of Component (A) and Component(B).